Physiologic Effects of Insulin :: essays research papers

Stand on a streetcorner and ask people if they know what insulin is, and legion(predicate) will reply, "Doesntit have whateverthing to do with blood sugar?" Indeed, that is correct, but such a response is a bit likesaying "Mozart? Wasnt he some kind of a musician?" Insulin is a key player in the control of intermediary metabolism. It has profound effectson both carbohydrate and lipide metabolism, and significant influences on protein andmineral metabolism. Consequently, derangements in insulin signalling have widespread anddevastating effects on many organs and tissues. The Insulin Receptor and Mechanism of Action homogeneous the receptors for other protein hormones, the receptor for insulin is embedded in the plasmamembrane. The insulin receptor is composed of two alpha subunits and two betasubunits linked by disulfide bonds. The alpha handcuffs are entirely extracellular and houseinsulin binding domains, while the linked beta chains penetrate through the plasma membrane. The insulin receptor is a tyrosine kinase. In otherwords, it functions as an enzyme that transfersphosphate groups from ATP to tyrosine residues onintracellular target proteins. Binding of insulin to thealpha subunits causes the beta subunits to phosphorylatethemselves (autophosphorylation), thus activating thecatalytic activity of the receptor. The spark off receptorthen phosphorylates a number of intracellular proteins,which in turn alters their activity, thereby generating abiological response. Several intracellular proteins have been identified asphosphorylation substrates for the insulin receptor, the best-studied of which is insulinreceptor substrate 1 or IRS-1. When IRS-1 is activated by phosphorylation, a lot of thingshappen. Among other things, IRS-1 serves as a type of docking center for recruitment andactivation of other enzymes that ultimately mediate insulins effects. A more detailed look atthese processes is presented in the section on Insulin Signal Transd uction. Insulin and Carbohydrate metamorphosisGlucose is liberated from dietary carbohydrate such as starch or sucrose by hydrolysis within thesmall intestine, and is then absorbed into the blood. Elevated concentrations of glucose inblood stimulate release of insulin, and insulin acts on cells thoughout the body tostimulate uptake, utilization and storage of glucose. The effects of insulin on glucosemetabolism vary depending on the target tissue. both important effects are Insulin facilitates entry of glucose into muscle, adipose and several other tissues.The only mechanism by which cells can take up glucose is by facilitated public exposure througha family of hexose transporters. In many tissues - muscle being a prime example - themajor transporter used for uptake of glucose (called GLUT4) is made available in theplasma membrane through the action of insulin.